Circuit breakers of this type are often installed in the open air and may be required to operate at very low temperature.
When a circuit breaker is filled with SF.sub.6 at a relative pressure of 5 bars and at 20.degree. C., there is a danger of the gas condensing when the outside temperature drops to -30.degree. C. The internal pressure drops to 2.3 bars at -50.degree. C.
These circumstances give rise to two types of drawback:
firstly, drops of liquid from the condensing gas which form on the inside walls of the circuit breaker (porcelain) may give rise to sparking between live components; and PA1 secondly, the low gas pressure, due to the low temperature, reduces the quality of the insulation in the circuit breaker and may lead to arcs restriking during circuit breaker opening.
One aim of the present invention is to provide a circuit breaker in which there is no danger of condensation taking place on the side walls of the circuit breaker.
Another aim of the invention is to provide a circuit breaker in which at least some of the condensed gas is evaporated in order to maintain the gas density at a level which is compatible with good circuit breaker operation.